pumping away from PONPC into the boiler

Randy Tibbits

I'm figuring a infloor and munchkin system. My design included a boilerpump, a primary loop pump, and infloor manifold pumps. The sales engineer from the company I deal with suggested I do away with the primary loop pump and use the boiler pump by it's self. The primary loop will be contained in the boiler room. Munchkin reccommends the boiler pump to be installed on the return side and in doing this I would install the air purger and expansion tank on the return side. I'm always willing to try something new however this seems weird to me. Any thoughts on this?

Steamhead

Depending on the fill pressure

if you pump away from a return-mounted tank into the Munchkin, you'll raise the pressure in the boiler and could cause the safety valve to open.

This may be the reason why the air separator and tank are shown on the primary loop, and the boiler is piped as a secondary loop.

For more, read Dan's books "Pumping Away" and "Primary-Secondary Pumping Made Easy".

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S Ebels

Correct Munchkin piping

Yes, pump into the boiler and away from the PONPC. Munchkin want to be sure to maintain a minimum 10 or 12 PSI in the boiler because of the pressure switch. When you pump away from the boiler, especially with a good sized circ on a primary loop, you can cause the static pressure to drop enough to lock out the switch. Not a happy thing.

Yes, use Pri-Sec piping. The Munchie has a fairly restrictive HX design with more than normal (think Cast Iron) head. If you put a circ on it that will satisfy the flow requirements for the HX, you will likely have a circ that is severly oversized for the flow through the rest of your heating system.

Get a Munchkin manual and look at the diagrams or call Chuck Shaw at HTP. He'll set you on the straight and narrow Munchkin way.

The sales engineer needs to do his homework a little better and find out a few of these thing for himself. Tell him to call HTP and get up to speed.

Mark Hunt

Viessmann


and the new Buderus pump into the boiler as well.

I think all of the low mass/low volume boilers want this?

Mark H

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Mark Eatherton1

Confusion explained...

In his book Pumping Away (available at books and more) Dan states that you should pump away from the PONPC and the boiler. This is because the PONPC IS the boiler in most cases, where the expansion tank is non captive and hung from the ceiling. It is perfectly acceptable to pump towards the boiler, AND away from the PONPC, provided that your static fill pressure and the pumps generative pressure capacity doesn't exceed 90% of the relief valves lifting threshold (typically 27 lbs).

I think the new condensing manufacturers are having us pump towards the boiler for a couple of reasons, the first and most important one being the pressure switch issue, and the second being that under certain conditions, the pumps can create enough of a low pressure condition that "boiling" at the fluid interface to the heat exchangers can occur, and makes some interesting noises. Think Whales in heat...

It is more important that you pump away from the PONPC than it is toward or away from the heat source. The heat source doesn't really care, nor do the manufacturers.

Hope this clears up the question.

ME